Microcontrollers, or microcontroller units (MCUs), are integrated circuits that are generally embedded in devices or products to control aspects of the device or product or monitor external events according to the software (firmware) running on the MCU. There is generally a desire to minimize the size of such devices, which has led to the miniaturization of MCUs.
However, an MCU requires a power source. This is typically provided by electrochemical cells, which may be galvanic cell batteries, such as alkaline, silver oxide, zinc-carbon and nickel cadmium cells. Each cell generally provides a maximum of about 1.2 to 1.5 volts. MCUs typically require up to 5 volts, which is generally provided by multiple cells. The desire to reduce size has led to the availability of ultra low power MCU families that utilize CMOS semiconductor technology. However, even these MCUs require at least 1.8 volts currently, and so require at least two cells connected in series, in the absence of voltage boosting circuitry. Also, it may be advantageous to use MCUs that require higher voltages for cost or other reasons.
One approach to allowing an MCU to operate with a single cell that has sufficient energy to power the MCU is to employ a voltage boosting circuit, also referred to as a DC-to-DC converter or a step-up voltage converter. Such converters generally fall into one of two categories: (1) those that switch the current flow through an inductor, and (2) those which that switch the current flow through a capacitor. The latter is often referred to as a “charge pump”. Many variants of these types of converters are known.
The use of a separate step-up voltage converter at least partially defeats the purpose of using the converter by increasing the size of the device as well as its cost and complexity.
Approaches have been disclosed where some elements of an inductor-based step-up converter are incorporated into an MCU chip. However they require an external inductor to operate, which increases the size of the device significantly. Such a solution also precludes ultra low power operation due to the current consumption of the boost circuit.